Multilayer composites of this type are employed in filter bags and bag filter installations. Bag filter installations are often used for the purification of dust-containing gases in power stations. In a bag filter installation, a plurality of filter bags are arranged. In this case, the filter bags are tension-mounted on a supporting body which is located on the clean gas side. When the flow passes through the filter bags from the crude gas side to the clean gas side, dust is retained on the crude gas side of the filter bag. The purified gas passes through the filter bag onto the clean gas side.
Filter bags of this type are clogged by a dust cake after a certain operating time. The dust cake is located on the side facing the crude gas side of the filter bag. The filter bags can then be cleaned off by means of pressure pulses from the clean gas side. As a result of these pressure pulses, the filter cake adhering to the filter bags comes loose and falls into a dust collection container on the crude gas side.
It is known to deposit a fiber nap as an upstream ply on a supporting ply. Nonwovens consisting of staple fibers are known as fiber naps. A nonwoven consisting of staple fibers is often connected thermally to the supporting ply and processed to form a laminate. This measure is necessary in order to give the multilayer composite a sufficient stability against pressure pulses. The upstream ply is to be prevented from coming loose from the supporting ply.
It is in this case a disadvantage that, due to the thermal bonding, the multilayer composite obtained, on the one hand, is brittle and difficult to move and, on the other hand, can be manufactured only in a complicated way.
Furthermore, for the manufacture of filter bags, multilayer composites consisting of one supporting layer and of two staple fiber nonwovens are often selected. In these, the staple fiber nonwovens are connected to the supporting layer and to one another by means of mechanical needling.
It is in this case a disadvantage that the multilayer composite has as a consequence of production penetration points which increase the permeability to dust particles. It is also a disadvantage that, in order to manufacture such a multilayer composite, only relatively coarse fibers with a fineness which allows a carding of the fibers can be used.